Ultra-low inter-channel crosstalk in array waveguide device incorporating self-assembled microsphere diffraction layer.

In array-type optical devices integrated on a single chip with high density, the crosstalk between adjacent devices causes main reason of limited transmission capacity in cascaded optical communication systems. In order to reduce the crosstalk in an arrayed variable optical attenuator, we incorporated a self-assembled monolayer of a microsphere array in the device. The microsphere array introduces a large index contrast in the polymer waveguide, thereby causing strong diffraction of the planar guided modes toward the surface normal directions. Due to the microsphere diffraction, the inter-channel crosstalk between the adjacent channels in a variable optical attenuator array decreases to less than -50 dB.